The present application is the national stage under 35 U.S.C. 371 of PCT/IL98/00629, filed Dec. 29, 1998.
The present invention is generally in the field of pulsed magnetic forming (PMF) and provides an apparatus and method for such forming. More particularly, the present invention relates to a PMF process forming of a dish from a planar plate.
Metal objects can be formed to have a desired shape by a variety of processes. For example, metal in a liquid form, can be molded to have the desired final shape. However, such a process is applicable in certain specific cases and in addition requires the expense of a large amount of energy and complicated and costly installations for heating and cooling.
Metal has some pliability and accordingly metalwork pieces of one shape can at times be formed to have another shape. For example, a metal plate can be formed and cut to have a wide variety of desired shapes by using a mechanical press. Such pressing methods require a very costly and large installations required for achieving the necessary pressure for attaining the desired final object.
PMF is a process in which a metal workpiece or a portion thereof is put into a rapid motion by pulse magnetic fields which causes the workpiece to deform. One advantage of the PMF process is in that energy loss in this process is minimal and consequently there is no or very little heating of the workpiece. In addition, this process does not have the disadvantage of leaving tool marks, as is the case in a variety of other techniques. The PMF process uses a discharge capacitor or a bank of capacitors, a forming coil and often a field shaper, for creating an intense transient magnetic field. Very intense magnetic fields created in the PMF process, is a result of the rapid discharge of electric energy, stored in the capacitors, through the forming coil. The resulting eddy currents that are induced in the workpiece yields a magnetic repulsion between the workpiece and the forming coil, which cause the workpiece to deform.
A background on prior art apparatuses and methods for working of metal workpieces by the PMF process can be found in U.S. Pat. Nos. 3,654,787, 3,961,739, 4,170,887, 4,531,393, 4,807,731, 5,353,617 and 5,442,846, and in PCT Application Publication No. WO 97/22426.
When forming a shaped metal object from a planar metal plate, it is necessary at times to both shape a plate to acquire a desired three-dimensional pattern and to trim the edges so as to define the boundaries of the shaped metal object.
It is an object of the invention to provide PMF forming apparatus and method for forming a metal plate into a dish having a desired three-dimensional pattern and shape.
The present invention provides, by a first of its aspects, an electromagnetic forming apparatus for forming an essentially planar metal plate into a dish having a three-dimensional pattern. A typical non limiting example of the invention is its application in the formation of a satellite dish from a planar plate.
In accordance with one embodiment, the apparatus comprises:
a mold having a forming surface with a contour corresponding to said three-dimensional pattern, and having edges corresponding to boundaries of the dish, which edges are defined by side walls essentially perpendicular to the forming surface;
a forming coil device opposite and proximal to said forming surface, and extending peripheral to said edges; the plate being
accommodated between the forming coil and said forming surface; and
an electric discharge circuitry for discharging a short and intense electric current pulse through the forming coil device to yield a pulsed magnetic forming (PMF) force for deforming said plate.
In accordance with one embodiment of the invention, the forming coil comprises a single coil member. In accordance with another embodiment of the invention, the forming coil device comprises an array of two or more coil members. The coil members in a forming coil comprising two or more coil members are typically concentric. An apparatus in accordance with this embodiment comprises:
a mold having a forming surface with a contour corresponding to said three-dimensional pattern;
a forming coil device opposite and proximal to said forming surface comprising two or more coil members; the plate being accommodated between the forming coil and said forming surface; and
an electric discharge circuitry, comprising two or more discharge circuitries, one associated with each coil member, for discharging short and intense electric current pulses through the coil members to yield pulsed magnetic forming (PMF) forces for deforming said plate.
In the case of a forming coil comprising two or more coil members, the discharge circuitries may be timed to discharge the current pulse through all coil members simultaneously; or advantageously, the discharge is timed in accordance with a predetermined discharge sequence. For example, in the case of several concentric coil members, the discharge sequence may be such so that it propagates from the central coils to the peripheral ones; in the reverse direction, namely from the peripheral ones towards the central ones; or in any other desired discharge sequence designed to obtain a certain three-dimensional pattern.
In accordance with another embodiment of the invention, the forming coil comprises one or more coil members which are displaceable along an axis essentially normal to a plane defined by the metal plate. The apparatus in accordance with this embodiment comprises:
a mold having a forming surface with a contour corresponding to said three-dimensional pattern;
a forming coil device comprising one or more coil members, displaceable along an axis essentially normal to a plane defined by the metal plate;
an electric discharge circuitry, comprising two or more discharge circuitries, one associated with each coil member, for discharging short and intense electric current pulses through the coil members to yield pulsed magnetic forming (PMF) forces for deforming said plate.
The forming coil in the apparatus according to this embodiment typically comprises two or more coil members separately displaceable along said axis. The deformation of the plate may comprise two or more steps. In the first step, the plate is partially deformed by a PMF force and then the coil members are displaced to an axial position corresponding to the displacement of the plate after the initial deformation. Then a PMF pulse is discharged again to further deform the plate, and this process may be repeated until the final shape has been attained.
In accordance with another embodiment of the invention, the forming coil device, which may comprise one or more coil members, has a size such that it covers only a portion of the plate to be deformed. An apparatus in accordance with this embodiment comprises:
a mold having a forming surface with a contour corresponding to said three-dimensional pattern;
a forming coil device opposite and proximal to said forming surface, and comprising one or more coil members having a size such that it covers only a portion of the plate to be deformed, the one or more coil members being displaceable in plane parallel to that of the plate;
an electric discharge circuitry for discharging a short and intense electric current pulse through each of the one or more coil members to yield a pulsed magnetic forming (PMF) force for deforming said plate.
In accordance with this embodiment, the forming coil member is first positioned at an initial position, a PMF pulse is generated to partially deform the opposite portion of the plate and then the forming coil is moved to another position opposite another portion of the plate whuch is then deformed by another PMF pulse. These steps are repeated untill the entire plate has been deformed to assume said there-dimensional pattern.
The mold, in accordance with one embodiment, comprises one or more depressions which correspond to said three-dimensional pattern. Typically, in accordance with this embodiment, the mold has a central concave portion, defining and serving as a template for a central concave portion of the dish. During deformation in which portions of the plate rapidly move into the depression, gases, e.g. air, remaining in the mold can resist the movement and thus prevent the obtaining of the desired three-dimensional shape. Accordingly, by one embodiment, gas-release ducts are provided to allow egression of gasses from the depression during this phase.. These may be connected to a vacuum source for removal of the gasses from the depression.
In accordance with another embodiment, the forming surface comprises bulges which define said three-dimensional pattern. In accordance with another embodiment of the invention, the forming surface comprises at least one depression and at least one bulge, which together define said three-dimensional pattern.
In accordance with another aspect the invention provides a method for electromagentic forming of a generally planar metal plate into a dish with a three-dimensional pattern. In accordance with one embodiment, the method comprises:
(a) providing a mold having a forming surface with a contour corresponding to said three-dimensional pattern, and having edges corresponding to boundaries of the dish, which edges are defined by side walls essentially perpendicular to the forming surface;
(b) placing the metal plate over the forming surface of the mold;
(c) providing a forming device coil connected to an electric discharge circuitry, and placing it over said metal plate, the forming coil extending beyond the edges of said forming surface; and
(d) discharging a short pulse of an intense electric current through said coil to shear the plate along said edges and forcing other portions of said plate to assume a shape defined by said mold, thus obtaining said dish.
In accordance with another embodiment the method comprises:
(a) providing a mold having a forming surface with a contour corresponding to said three-dimensional pattern;
(b) placing the metal plate over the forming surface of the mold;
(c) providing a forming coil device, comprising two or more forming coil members each of which being connected to an electric circuitry, and placing the forming coil device over said metal plate;
(d) discharging a short pulse of an intense electric current through said two or more coil members to deform said metal plate;
(e) displacing said coil members along said axis to a position corresponding to the shape of the plate after the deformation and repeating step (d);
(f) repeating step (e) until attainment of said three-dimensional pattern.
In accordance with a further embodiment of the invention, the method comprises:
(a) providing a mold having a forming surface with a contour corresponding to said three-dimensional pattern;
(b) placing the metal plate over the forming surface of the mold;
(c) providing a forming coil device which comprises one or more coil members having a size such that it covers only a portion of the plate to be deformed, the one or more coil members being displaceable in a plane parallel to that of the plate, and placing the forming coil device over said metal plate;
(d) discharging a short pulse of an intense electric current through said coil to deform portions of the plate opposite said forming coil device;
(e) laterally displacing said forming coil device and repeating step (d);
(f) repeating step (e) until said three-dimensional pattern has been attained.
The invention will now be illustrated by describing some non-limiting specific embodiments depicted in the annexed drawings: